Spark-gap device having a thin conductive layer for stabilizing operation

ABSTRACT

A SPARK-GAP DEVICE INCLUDES FIRST AND SECOND ELECTRODES AND AN INSULATING SPACER SEPARATING THE TWO. ALONG THE INSULATING SPACER IS DISPOSED AN ELONGATE CONDUCTIVE LAYER IN INITMATE CONTACT WITH THE SPACER AND ELECTRICALLAY CONNECTED TO A FIRST OF THE ELECTRODES. THE CONDUCTIVE LAYER, WHICH IS NARROW COMPARED TO THE ACTIVE PART OF THE ELECTRODES WHERE ARCING TAKES PLACE, EXTENDS FROM THE FIRST ELECTRODE TOWARD THE SECOND, BUT IS SPACED FROM THE SECOND BY A DISTANCE GREATER THAN THE GAP SPACING BETWEEN THE ELECTRODES.

United States Patent [72] Inventor Chester J. Kawiecki [56] References Cited Sam Barbara Calii- UNITED STATES PATENTS f Qf 2 2.924,?34 2/1960 Lapple 313/307x -3 d 1971 3.111.606 11/1963 Schultzetal... 315/36x 5"": a d S I, C 3,328,632 6/1967 Robinson 1 a 313/307x l 1 f f 3.431.452 3/1969 Hale et al a 1 ..3 313/313x 3,454,811 7/1969 Scudner 313/325x Primary Examiner-John W. Huckert Assistant Examiner-Andrew J1 James A11orneysBuckhorn, Blore, Klarquist and Sparkman [54] SPARK-GAP DEVICE HAVING A THIN CONDUCTIVE LAYER FOR STABILIZING ABSTRACT: A spark-gap device includes first and second aims, rawlng lg electrodes and an insulating spacer separating the two. Along [52] 11.8. C1 313/306, the insulating spacer is disposed an elongate conductive layer 313/242, 313/308, 313/325, 315/35, 317/61 in intimate contact with the spacer and electrically connected [51 Int. Cl H0lj 1/46, to a first of the electrodes. The conductive layer, which is nar- I-[01j 21/10 row compared to the active part of the electrodes where are- [50] Field of Search 313/150, ing takes place, extends from the first electrode toward the second,' but is spaced from the second by a distance greater than the gap spacing between the electrodes.

1e are i PATENTEDJUH28I9TI 3588.576

sum 1 0F 2 CHESTER J. KAWI 5cm INVENTOR BY BUCKHOR/V, BLOHE, KLAROU/ST 5 SPARK/VAN ATTORNEYS SPARK-GAP DEVICE HAVING A THIN CONDUCTIVE LAYER FOR STABILIZING OPERATION BACKGROUND OF THE INVENTION Spark-gap devices, e.g. for protecting lines and equipment from high voltage surges, are frequently erratic in their response to high voltage ramps. These devices tend to be slow in breaking down and therefore will frequently not respond to a fast-rising transient surge until the line voltage reaches an undesirably high value. After a gap has been in service for an appreciable length of time and arcing has occurred therein, both the breakdown voltage and the response time tend to decrease. Therefore, in order to stabilize operation in such a device, some gaps are preconditioned by firing the gaps a number of times before placing them in service. However, preconditioning in this way tends to reduce the subsequent life of the device. I

SUMMARY OF THE INVENTION According to the present invention, the insulating means of a spark-gap device is spaced from the region of the gap, and an elongate conductive layer'is adhered to the insulating means at the time of manufacture.'This conductive layer is quite slender or narrow as compared with the active part of the elec-' trodes where arcing takes place, and is intimately adhered to the insulating spacer. It is also desirably connected to one of the electrodes while being spaced from the other electrode by a distance greater than the gap spacing of the device. The conductive layer may comprise, for example. a graphite line inscribed upon the insulating spacer during manufacture of the spark-gap device. It has been found that a device including this elongate conductive layer has stabilized operating characteristics from its initial manufacture, and furthermore has much faster response as compared with other devices. The improved characteristics are believed due to the concentration of electric field produced by the elongate conductive layer.

It is accordingly an object of the present invention to provide an improved spark-gap device having a faster response.

It is another object of the present invention to provide an improved spark-gap device having improved response to high rates of voltage rise.

It is another object of the present invention to provide an improved spark-gap device which is of economical manufacture and which may be placed in service without precondition firing.

It is another object of the present invention to provide an improved spark-gap device characterized by stable operating characteristics.

It is another object of the present invention to provide an improved spark-gap device exhibiting a longer operating lifetime.

The subject matter which I regard as my invention is particulatly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, both as to organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference characters refer to like elements.

DRAWINGS FIG. I is a longitudinal cross-sectional view of a spark-gap device according to the present invention;

FIG. 2 is an end view ofthe FIG. I device;

FIG. 3 is a longitudinal cross section of a modified version of the FIG. I spark-gap device;

FIG. 4 is a longitudinal cross section of a double gap arran'gement of the FIG. ll type;

FIG. 5 is a view taken at 5-5 in FIG. I illustrating an elongate conductive layer or line employed in the spark-gap device of the present invention; I

FIG. 6 is a longitudinal cross section of the FIG. 1 spark-gap device illustrating electric field lines as may be associated with the device.

FIG. 7 is another longitudinal cross section of the FIG. 1 device taken at 7-7 in FIG. 1, and further illustrating the electric field configuration;

FIG. 8 is a longitudinal cross section of a second embodiment of the present invention;

FIG. 9 is a longitudinal cross section of the third embodiment of the present invention; and

FIG. 10 is a curve plotting voltage-time conditions for breakdown of a spark-gap device according to the present invention. 7

DETAILED DESCRIPTION Referring to the drawings, and particularly to FIGS. 1 and 2,

a spark-gap device according to the-present invention includes an insulating spacer member comprising cylindrical ceramic spacer tube 10 which is suitably approximately five-sixteenths inch in diameter by approximately five-sixteenths inch in length. The ceramic spacer tube 10 is suitably alumina. In as sembling the device according to the present invention, the ends of ceramic spacer tube 10 are metallized as indicated at 12 and 14, and brazing washers l6 and 18, which may be formed of copper or an alloy of copper and silver, are located on the metallized ends. Then, thin walled hollow electrodes 20 and 22, preferably formed of a nickel, iron, cobalt alloy having a coefficient of expansion compatible to that of alumina, are inserted into either end of the ceramic tube to complete a chamber or enclosure 25. The chamber, thus formed, is suitably later provided with an atmosphere of a gas selected according to-the operational characteristics desired. For example, the gas may be at less than atmospheric pressure.

The electrodes comprise conductive means according to the present invention, and are provided with first and second electrode end portions 26 and 28, respectively, which are juxtaposed to provide a gap 30 therebetween for supporting an arc discharge. The electrode end walls adjacent the gap are suitably slightly cup-shaped or concave where they face one another to give structural strength to the end portions.

The electrodes 20 and 22 are substantially cylindrical toward electrode end portions 26 and 28 and are spaced inwardly from spacer tube 10 at this point. However, toward the ends of spacer tube 10, the electrodes 20 and 22 are flared outwardly and rearwardly, being provided with radial flanges 24 at their outermost ends for making contact with brazing washers l6 and 18. To secure the electrodes 20 and 22 within spacer tube 10, the assembly of these components, with brazing washers 16 and 18 in place, is suitably raised in temperature to braze the assembly. A spark-gap of this configuration is set forth in my copending application Ser. No. 684,706 entitled Surge Protector" filed Nov. 21, 1967, and assigned to the assignee of the present invention.

The spark-gap device is further provided with elongate conductive layers 32 and 34 adhered to ceramic tube 10 in intimate contact therewith, and in electrical contact respectively with electrodes 20 and 22. Thus, conductive layer 32 makes electrical contact with brazing washer I6 while conductive layer 34 makes contact with brazing washer 18. Each of these conductive layers is quite slender or narrow as compared with the diameter of electrode end portions 26 and 28 and extend from one electrode toward the other, terminating short of the other electrode with a spacing greater than the spacing of gap 30. Thus, it is not intended that an arc breakdown shall take place between the conductive layer 32 and electrode end portions 28, for example. Therefore, the right end of conductive layer 32 (as viewed in FIG. 1) extends to a position adjacent the gap area, but does not extend so close to any portion of electrode 22, including the electrode end portion thereof or the outwardly flared portion thereof, that an arc would be established between the layer 32 and electrode 22.

In this instance, an elongate conductive layer extends along theinner side of ceramic tube 10 from each electrode toward the opposite electrode, terminating substantially adjacent the gap 30. The elongate conductive layers 32 and 34 are also desirably positioned opposite one another, or from one another inside tube 10, although the latterpositioning is not critical. The opposite location of the conductive layers principally avoids breakdown therebetween. While two conductive layers are desired, one extending from each electrode, in order to provide symmetrical operating characteristics for the spark-gap device, only one such layer may be employed if so desired. Of course, a greater number than two maybe employed, properly spaced from one another, but this leads to little, if any, additional advantage.

Referring more particularly to FIG. 5, illustrating the inner surface of ceramic tube It) with an elongate conductive layer 34 adhered thereto, it is seen the elongate conductive layer 34 is substantially linear, extending longitudinally of the sparkgap device. This configuration is the simplest and easiest, but the conductive layer need not be straight. For example, it may describe a helical path around the interior of tube if desired. The layer 34 is satisfactorily produced as a graphite line inscribed or drawn upon the ceramic tube. The line may also be provided in a plurality of other ways. For example, a strip corresponding to layer 34 may be metallized, and then a thin metal, e.g. copper or silver, conductor may be brazed thereto. Alternatively, graphite or some metal such as silver may be painted in a proper liquid carrier upon the ceramic to provide layer 34. In the device of FIG. 11, a line having a width of about 0.015 to 0.030 inch has proven to be satisfactory. In any case, such a coating or metallic layer must be substantially bonded to the refractory ceramic material in intimate relation thereto. For example, merely placing a conductor in physical contact with the interior of the ceramic has not been found to produce satisfactory results as compared with the intimately contacting layer. In the case of a glazed ceramic, the glaze is removed by grinding in the area where the elongate conductor is desired before inscribing or otherwise providing such layer thereupon.

The employment of the conductive layer as thus described results in reduction in breakdown time to high rates of voltage rise. Moreover, the response time of the gap to high voltage rise remains substantially constant over the life of the device.

In FIG. 10 there is plotted a first curve 36 for a device without an elongate conductive layer, while curve 38 is plotted for the device with the elongate conductive layer. These curves indicate the locus of points describing arc breakdown conditions across the gap, relating voltage to time. For example, in the instance of either curve, when a low 'rate of rise is applied across the gap, i.e. between electrodes and 22, breakdown occurs at a lower voltage and a greater time is required for breakdown. However, in the case of the gap employing the elongate conductive layer, both the voltage and time factors are reduced as illustrated by the lower curve. For example, identical spark-gap devices were tested, one with the elongate conductive layer, and one without the elongate conductive layer. For the case of a 10 kilovolts per microsecond surge applied to a nominal 250 volt DC static breakdown gap device, the breakdown voltage without an elongate conductive layer was 3,000 volts. By adding such a layer, the breakdown occurred with the applied voltage had reached no more than 500 volts. It is thus seen that the gap device of the present invention gives significantly improved protection from high voltage surges.

It is postulated that the improved results regarding breakdown voltage and speed of response are attained as a result of the electric field concentration provided by the elongate conductive layer. The electric field concentration assists rapid ionization in the gap region. FIGS. 6 and 7 are partially broken away cross-sectional views of the spark-gap device on which electric field lines are illustrated for the vicinity of the gap. These views are taken in planes separated from one another by 90. Electric field lines extend from the ends of conductive layers 32 and 34 toward the opposite electrode as indicated at 36 and 37in FIGS. 6 and 7. To obtain the maximum concentration, it thus appears desirable that the elongate conductive layer be narrowest in the vicinity of gap 30, e.g. at least at the end of said layer remote from the electrode to which it is connected.

FIG. 3 illustrates an alternative embodiment of the present invention wherein like elements are referred to by primed reference numerals. Construction is the same except for elongated conductive member 38 extending longitudinally of the device along the inner wall of ceramic tube 10'. In this instance, conductive layer 38, bonded to the. ceramic tube 10', extends from the vicinity of one conductive means to the vicinity of the other conductive means, but is connected to neither. Conductive means 38 is also narrow in comparison to the diameter of electrode end portion 26', and 28', e.g. the portion of means 38 adjacent gap 30'..The spacings between conductive layer 38 and each of the electrodes 20' and .22 should total a distance greater than the spacing of gap 30' so as to avoid a breakdown path including layer 38. While the FIG. 3 construction is of some utility, the construction hereinbefore described in connection with FIG. 1 is preferred because of improved results obtained therewith.

FIG. 4 illustrates a further embodiment of the present invention including a pair of spark-gap devices in series, each of which has the same general configuration of a FIG. 1 device. The first spark-gap device of FIG. 4 includes electrodes 40 and 42 separated by ceramic spacer tube 44. Longitudinally joined to the first device is a second spark-gap device including electrodes 46 and 48 separated by ceramic spacer tube 50. Electrodes 42 and 46 are joined together at their flanged ends by means ofa brazing washer 52. The end walls of electrodes 42 and 46 adjacent gaps 54 and 56 are apertured whereby illumination produced by an arc breakdown at one gap radiates the other for assisting ionization and simultaneous breakdown of the second gap. Chamber 58 is formed within joined electrodes 42 and 46 and assists in extinguishing the arcs when an overvoltage condition is no longer present. This general construction is set forth in my copending application, Ser. No. 713,919, entitled, Spark-Gap Device, filed Mar. 18, 1968, and assigned to the assignee of the present invention.

In the FIG. 4 device, first and second elongate conductive layers 60 and 62 extend from electrodes 40 and 48, respec tively, toward gaps 54 and 56. The employment of a single conductive layer at each end of the device has been found satisfactory to attain symmetrical operating characteristics for the device when it is connected across lineo-line or line-toground, However, if the device is to be utilized with center electrodes connected to a third conductor (generally this would be ground), to render the device elecirically symmetrical, conductive layers from electrodes 42, 46 should also be provided. Construction is otherwise as herein described for the embodiment of FIG. 1.

Another embodiment of the present invention is illustrated in FIG. 8, this gap being larger in size and heavier than the gap structures hereinbefore disclosed. A first electrode 64 comprises a conductive means according to the present invention, here including a threaded rod 66 provided with an electrode end portion 68. Electrode end portion 68 is secured to end plate 70, the latter being provided with an axial flange 72 for receiving an end of ceramic spacer member or tube 74 therewithin. The ceramic spacer tube is sealed to flange 72 by means of metal bellows 76 soldered to a metallized portion of the spacer tube.

A second electrode 78 including conductive means 80 in the form of a threaded rod is provided with electrode end porti on 82 spaced from electrode end portion 68 to provide a gap 84 therebetween. Threaded rod 80 is received in hub 86 secured to cap 88 which also forms a metal bellows. Cap 88 is suitably soldered to ceramic tube 74, the latter being metallized at this location to form the connection. A nut 90 is received upon threaded rod 66 and secures end plate 70 upon .conductive support 92. Conductive support 92 provides a connection to the device. Similarly, nuts 94, received on threaded rod 80, secure rod 80 to conductive support 96, the latter providing the other connection to the device.

Conductive layers 98 and I00 are provided on the inside of ceramic tube 74, respectively making contact with bellows 76 and end cap 88. These conductive layers are formed in the same manner as hereinbefore described in connection with previous embodimentsand extend along the interior of the ceramic tube to locations adjacent, and on opposite sides of, gap 84, for acting to concentrate the electric field. The conductive layers are narrow in comparison to the diameter of the electrode end portions, For example the conductive layers are about one-sixteenth inch in width whereas end portion 68 has a diameter, d, of three-eighths inch in a device constructed as shown. The conductive layers do not extend far enough toward the opposite electrode so the spacing therebetween is as small as the spacing of gap 84, whereby the danger of arcing to the conductive layers is minimized.

Referring to FIG. 9, a spark-gap device construction is illustrated wherein ceramic tube 102 is located interiorly of conductive means of one electrode. Thus, ceramic tube 102 is joined by means of metal bellows 104 to a cylindrical metal housing, 107, coaxially disposed around ceramic tube 102. Ceramic tube 102 receives therewithin a threaded rod 108 extending longitudinally therethrough and providing conductive means for an electrode including an end portion 108 threadably secured to rod 106 at the end of ceramic tube 102. Housing 107 is internally threaded at the end thereof remote from bellows 104 and receives a threaded metal plug 110 comprising conductive means for an electrode and also including electrode end portion 112 disposed adjacent electrode end portion 108 to provide a gap 114 therebetween. Plug 110 is also secured to a conductive support 114 by means of a threaded stud 116, threadably secured within a tapped recess in plug 110, and receiving nut 118 drawn up on the opposite side of conductive support 114.

Threaded rod 106 threadably engages retaining nut 120 drawn up against axially flanged washer 122 through an aperture in end cap 124, the latter being joined to ceramic tube 102. Nut 126, also received on threaded rod 106, is drawn up against retaining nut 120, and furthermore, a nut 128 received upon rod 106 secures the same to conductive support 130. The conductive supports in each case provide end connections for the spark-gap device.

The portion of ceramic tube 102 within enclosure 132 completed by housing 107 and plug 110 is spaced from the inner wall of housing 106. This portion of the spacer tube is provided with an elongate conductive layer 134 making contact with bellows 104 and extending toward electrode end portion 108. One Hundred eighty degrees around the spacer tube 102, the spacer tube is provided with another elongate conductive layer 136 making connection with electrode end portion 108 and extending toward bellows 104. The conductive layers are again substantially narrower than the electrode end portions and are each connected to one of the electrode structures while extending toward the other electrode structure. However, they do not extend far enough toward the opposite electrode structure such that the spacing between the conductive layer and the opposite electrode structure equals that of gap 114.

The construction of P16. 9 illustrates the fact that the elongate conductive layers do not have to be immediately adjacent the gap, as long as the elongate conductive layer is located within the same enclosure or ionizable region as the gap. The conductive layer is again intimately adhered to the ceramic spacer. While a pair of elongate conductor layers are employed, it is possible to utilize only one such layer if desired.

The NO. 9 structure is also utilizable within a double ended construction such as generally set forth in U.S. Pat. No. 3,388,274 issued June 1 l, 1968, to Chester J. Kawiecki and Walter T. Pranke, Jr. This patent is entitled, Axial Spark Gap with a Coaxial Third Electrode Adjacent the Main Axial Electrodes," and is assigned to the assignee of the present invention. In this instance, one or two conductive layers may be applied as described to the internal portions of the ceramic cylinders or tubes located at each end of the double device.

1 claim:

1. A spark-gap device comprisingi first and second conductive means respectively including first and second conductive electrode end portions spaced from one another to define a gap therebetween for supporting an arc discharge, and an insulating member;

said conductive means and said insulating member defining an ionizable region including said gap; and

wherein said insulating member is provided with an elongate conductive layer disposed along said insulating member within said ionizable region, at least a length of said conductive layer comprising a conductive line having a width across said insulating member and over some appreciable length of said conductive line which width is substantially narrower than said conductive electrode end portions.

2. The device according to claim 1 wherein said elongate conductive layer extends adjacent said gap in spaced relation thereto.

3. The device according to claim 1 wherein said elongate conductive layer is electrically ductive means.

4. The'device according to claim 1 wherein said elongate conductive layer extends along said insulating member from the vicinity of one conductive means to the vicinity of the other conductive means but is connected to neither.

5. The device according to claim 1 wherein said elongate conductive layer comprises a graphite line inscribed upon said insulating member.

. 6. A spark-gap device comprising:

first and second conductive means respectively including first and second conductive electrode end portions spaced from one another to define a gap therebetween for supporting an arc discharge; and an insulating spacer member between said conductive means for insulating the conductive means from one another while positioning one of the said electrode end portions adjacent the other, said insulating member being spaced from said gap,

said conductive means and said insulating member defining a closed chamber including said gap; wherein said insulating member is provided with an elongate conductive layer adhered to said insulating member in intimate contact therewith and in electrical contact with said first conductive means, said layer extending within said chamberfrom said first conductive means toward the second conductive means while terminating short of the second conductive means by a distance greater than the spacing of said gap, at least a portion of said conductive layer having a width across said insulating member and over a length of said conductive layer which width is substantially narrower than the said conductive electrode end portions.

7. The device according to claim 6 wherein said insulating spacer member comprises a substantially cylindrical enclosure joined to said firstand second conductive means for locating said electrode end portions within said cylindrical enclosure.

8. The device according to claim 7 wherein said spacer member is formed of ceramic material.

9. The device according to claim 7 wherein each of said conductive means extends longitudinally into said cylindrical enclosure from an end periphery thereof, each said conductive means having a reduced diameter toward said electrode end portions such that said cylindrical enclosure is spaced from said gap, said conductive layer extending along the inside wall of said cylindrical enclosure to a position substantially adjacent said gap.

10. The device according to claim 6 wherein said insulating spacer member is located axially on the opposite side of one of said electrode end portions from the other electrode end portion.

11. The device according to claim 6 wherein said second conductive means is coaxially disposed around at least a portion of said first conductive means with the electrode end portion of the first conductive means being located inside said second conductive means, said insulating spacer member coaxially separating said first and second conductive means connected to one of said conwhile having at least a portion thereof within said second conductive means in spaced relation from an inner wall of said second conductive means, said elongate conductive layer being adhered along the surface of the portion of said insulating member located within the second conductive means.

12. The device according to claim 6 further including a second elongate conductive layer adhered to said insulating member in intimate contact therewith and in electrical contact with said second conductive means, said layer extending within said chamber from said second conductive means toward the first conductive means while terminating short of the first conductive means by a distance greater than the spacing of said gap, at least a length of said second elongate conductive layer being substantially narrower than the said conductive electrode end portions, said second elongate conductive layer also being spaced from the first elongate conductive layer by a distance greater than the spacing of said-gap.

13. The device according to claim 12 wherein said first and second elongate conductive layers are disposed opposite one another within said insulating spacer member.

14. The device according to claim 6 wherein said elongate conductive layer comprises a conductive line which is no more than one-fifth the width of said electrode end portions.

15. The device according to claim 6 wherein said elongate conductive layer comprises a graphite line inscribed upon said insulating spacer member.

16. The device according to claim 6 wherein said elongate conductive layer is substantially narrower than said conductive electrode end portions at least at the end of said layer remote from said first conductive means.

17. The device according to claim 6 wherein said elongate conductive layer is substantially narrower than said conductive electrode end portions at least alonga portion of said elongate conductive layer most closely spaced to said gap.

18. The device according to claim 6 wherein said elongate conductive layer comprises a length of metal bonded to said insulating spacer member.

19. The device according to claim 17 wherein said elongate conductive layer comprises a metallized coating upon said insulating spacer member.

20. The device according to claim 6 wherein said closed chamber includes a gas at less than atmospheric pressure. 

